Problem: $ { {4} \times \left[\begin{array}{rr}{3} & {1} \\ {0} & {-2}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{4}\times{3} & {4}\times{1} \\ {4}\times{0} & {4}\times{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{12} & {4} \\ {0} & {-8}\end{array}\right]}$